pkg/shelf: change helper method on Request and Response

pkg/shelf/lib/src/message.dart

Index: pkg/shelf/lib/src/message.dart
diff --git a/pkg/shelf/lib/src/message.dart b/pkg/shelf/lib/src/message.dart
index 1b2e966c4660b3375519c985a459362257e00408..b4beef89c058496aca2748196e2fa7c84d4d9374 100644
--- a/pkg/shelf/lib/src/message.dart
+++ b/pkg/shelf/lib/src/message.dart
@@ -43,9 +43,10 @@ abstract class Message {
   /// If [headers] is `null`, it is treated as empty.
   Message(this._body, {Map<String, String> headers,
         Map<String, Object> context})
-      : this.headers = _getIgnoreCaseMapView(headers),
-        this.context = new pc.UnmodifiableMapView(
-            context == null ? const {} : new Map.from(context));
+      : this.headers = new _ShelfUnmodifiableMap<String>(headers,
+            ignoreKeyCase: true),
+        this.context = new _ShelfUnmodifiableMap<Object>(context,
+            ignoreKeyCase: false);
 
   /// The contents of the content-length field in [headers].
   ///
@@ -112,18 +113,86 @@ abstract class Message {
     if (encoding == null) encoding = UTF8;
     return Chain.track(encoding.decodeStream(read()));
   }
+
+  /// Creates a new [Message] by copying existing values and applying specified
+  /// changes.
+  Message change({Map<String, String> headers, Map<String, Object> context});
+}
+
+/// Returns a [Map] with the values from [original] and the values from
+/// [updates].
+///
+/// For keys that are the same between [original] and [updates], the value in
+/// [updates] is used.
+///
+/// If [updates] is `null` or empty, [original] is returned unchanged.
+Map updateMap(Map original, Map updates) {
+  if (updates == null || updates.isEmpty) return original;
+
+  return new Map.from(original)
+      ..addAll(updates);
 }
 
-/// Creates on an unmodifiable map of [headers] with case-insensitive access.
-Map<String, String> _getIgnoreCaseMapView(Map<String, String> headers) {
-  if (headers == null) return const {};
-  // TODO(kevmoo) generalize this model with a 'canonical map' to align with
-  // similiar implementation in http pkg [BaseRequest].
-  var map = new LinkedHashMap<String, String>(
-      equals: (key1, key2) => key1.toLowerCase() == key2.toLowerCase(),
-      hashCode: (key) => key.toLowerCase().hashCode);
+/// A simple wrapper over [pc.UnmodifiableMapView] which avoids re-wrapping
+/// itself.
+class _ShelfUnmodifiableMap<V> extends pc.UnmodifiableMapView<String, V> {
+  /// If `true`, the keys will have case-insensitive access.
+  final bool ignoreKeyCase;

[nweiz, 2014/04/30 20:21:39]

This shouldn't be public.

[kevmoo, 2014/05/02 16:18:01]

Done.

 
-  map.addAll(headers);
+  /// If [source] is a [_ShelfUnmodifiableMap] with matching [ignoreKeyCase],
+  /// then [source] is returned.
+  ///
+  /// If [source] is `null` it is treated like an empty map.
+  ///
+  /// If [ignoreKeyCase] is `true`, the keys will have case-insensitive access.
+  ///
+  /// [source] is copied to a new [Map] to ensure changes to the paramater value
+  /// after constructions are not reflected.
+  factory _ShelfUnmodifiableMap(Map<String, V> source,
+      {bool ignoreKeyCase: false}) {
+    if (source is _ShelfUnmodifiableMap<V> &&
+        source.ignoreKeyCase == ignoreKeyCase) {
+      return source;
+    }
+
+    if (source == null || source.isEmpty) {
+      return new _EmptyShelfUnmodifiableMap<V>(ignoreKeyCase);
+    }
+
+    if (ignoreKeyCase) {
+      // TODO(kevmoo) generalize this model with a 'canonical map' to align with
+      // similiar implementation in http pkg [BaseRequest].
+      var map = new LinkedHashMap<String, V>(
+          equals: (key1, key2) => key1.toLowerCase() == key2.toLowerCase(),
+          hashCode: (key) => key.toLowerCase().hashCode);
+
+      map.addAll(source);
+
+      source = map;
+    } else {
+      source = new Map<String, V>.from(source);
+    }
+
+    return new _ShelfUnmodifiableMap<V>._(source, ignoreKeyCase);
+  }
+
+  _ShelfUnmodifiableMap._(Map<String, V> source, this.ignoreKeyCase)
+      : super(source);
+}
+
+/// An const empty implementation of [_ShelfUnmodifiableMap].
+class _EmptyShelfUnmodifiableMap<V> extends pc.DelegatingMap<String, V>
+    implements _ShelfUnmodifiableMap<V>  {
+  final bool ignoreKeyCase;

[nweiz, 2014/04/30 20:21:39]

Once [ignoreKeyCase] is no longer public, there's no reason for this to have the
property at all.

[kevmoo, 2014/05/02 16:18:01]

Done.

+
+  /// Returns one of two const values for [_EmptyShelfUnmodifiableMap] depending
+  /// on the value for [ignoreKeyCase].
+  factory _EmptyShelfUnmodifiableMap(bool ignoreKeyCase) {
+    if (ignoreKeyCase) {
+      return const _EmptyShelfUnmodifiableMap._(true);
+    }
+    return const _EmptyShelfUnmodifiableMap._(false);
+  }
 
-  return new pc.UnmodifiableMapView<String, String>(map);
+  const _EmptyShelfUnmodifiableMap._(this.ignoreKeyCase) : super(const {});
 }